Win through before onset of vocal trouble (7)
I believe the answer is:
prevail
'win through' is the definition.
(I've seen this before)
'before onset of vocal trouble' is the wordplay.
'before' becomes 'pre' (prefix meaning 'before').
'onset of' suggests taking the first letters.
'trouble' becomes 'ail' (synonyms).
The initial letter of 'vocal' is 'v'.
'pre'+'v'+'ail'='PREVAIL'
(Other definitions for prevail that I've seen before include "Have opinion accepted" , "Carry the day" , "come out on top" , "Triumph, overcome" , "get the upper hand" .)